Cork recovery



United States Patent C CORK RECOVERY William G. Van Beckum, San Mateo, and Robert W. Miller, Scotia, Califi, assignors to The Pacific Lumber 1(\I Iornpany, San Francisco, Caiih, a corporation of ame No Drawing. Application August 34}, 195d Serial No. 606,974

6 Claims. Cl. 162 -21 This invention relates to the treatment of cork-containing, woody material to separate the cork from the noncork material. More particularly this invention relates to recovery of cork from bark containing cork mixed with fibrous material.

Commercial supplies of cork, both today and since the inception of the cork industry, have come almost exclusively from the cork oak, Quercus suber. Commercial stands of that species of oak are limited almost entirely to an area bordering on the Mediterranean. The great majority of commercial cork comes from Spain, Portugal and North Africa.

Cork is the outer bark of the cork oak, i.e., thedead part of the bark overlying the inner living bark. This outer layer is stripped from time to time. After suitable processing, such as sorting into grades and boiling, it passes into channels of trade.

There exist many uses of co'rk all of which depend upon some one or more of the properties of the material. These properties include a high degree of buoyancy, a high degree of compressibility without lateral spreading, a high resilience, resistance to moisture and liquid penetration, a high co'efficient of friction, a low thermal conductivity, a high ability to absorb mechanical and acoustical vibrations and a high degree of stability and resistanceto deterioration.

Thus-bottle stoppers (the corks of common parlance) rely upon resilience, compressibility and resistance to i liquid penetratio'n. Cork insulation, which is made by grinding cork to small particle size and bonding the particles" together byheat and pressure, utilizes the low thermal conductivity-of cork. Composition cork is made by similarly grinding cork into small particles which, however, are bonded together by added adhesive. It has many uses such as' gaskets, liners for'cro'wn'top bottle stoppers, inner soles of shoes, etc. Mere mention of theseuses' will bring to mind'the qualities of cork which make that material so versatile and useful Another use of cork is in linoleum, wherein linseed oil is'used to impregnate very finely divided cork known as cork flour.

In all its uses the cellular character of. cork is a The literature on the subject of cork indicates that all cork of any consequence comes from Qzzercus saber grown. in the Mediterranean area; that the transplated species, i.e., trees plantedinother parts of the world, are of no commercial consequenceyand that other species, of cork-bearing trees have been,. at best, minor sources of an-inferi'or product. The prevailing view is summedup by Faubel in Cork and the American Cork Industry,

Patented Feb. 23, 1960 published by Cork institute of America, rev. ed., page i, as follows:

For reasons which Nature alone controls, this oak tree grows in commercial stands only in areas bordering the Mediterranean Sea and all atempts to establish cork forests in this country and elsewhere have thus far been unsuccessful.

Such authorities as Faubel fail even to mention the known fact that cork exists in large proportion combined with fibrous and amorphous material in the bark of other trees, such as Douglas fir. The lack of commercial methods for separating the cellular cork from the fibrous and amorphous material in such barks explains the fact that, by and large, the literature on cork does not even mention cork-bearing Douglas fir bark and the like as a potential source of co'rk.

It is a known fact (cf. Kurth in Journal Forest Products Research Society, vol. 1, pp. 98-103 (1951)), that Douglas fir bark contains 25 to cork. In TAPPI, vol. 35, No. 2, February 1952, it is stated that cork may occur in the bark of the lower parts of mature Douglas fir trees in amounts exceeding 50%.

Douglas fir bark and other cork-containing barks are stripped from saw, pulp and other logs in vast quantities and are a potential source of very large amounts of cork. Work has been done on the recovery of cork from such barks, as described in more detail below, but by and large these barks have very limited value being used, for example, largely as fuels.

Previous efiorts to separate cork from noncork material in bark have employed mechanical attrition, such as ball milling or hammer milling. By such means it is supposed that the fibrous material, being more friable when in somewhat dry condition than the cork, would disintegrate to a greater degree than the cork. The object of these prior methods has been to separate the fibrous and amorphous noncork material as fine particles, and to selectively concentrate the cork in the coarser particles.

Whatever the merits of mechanical attrition, it is defective in practice because, among other things, the cork particles are flattened and compacted and are substantially reduced in size and resiliency by the impact of the milling elements. These reductions are serious deterrents to the quality of'cork'.

It is an object of the invention to provide an improved method of separating cork from nonco'rk materials in natural products such as bark.

It is another object of thepresent invention to provide a method ofseparatingcork from noncork material in naturalv products, particularly bark, such method being of a nature that it does a minimum of damage to the porous, cellular character of the cork and in fact, in some important respects improves it. 7

Itis a particular object of the invention to provide a method of treatingv Douglas fir bark to obtain fractions thereof which are high-v in cork. content, such method avoiding the. necessity and disadvantages ofmilling operations.

These and other objects of the invention will be apparent from the ensuing description and the appended claims.

In accordance with the invention, a natural product such as bark,.e.g., Douglas fir bark is selected which contains corky and noncorky material, the latter being usually of a fibrous and amorphous character. Such product is reduced to-a suitable size for harniling, if that is necessary, by shredding, cutting orthe like. his then subjected to the action of steam at high pressureand temperature. The steam pressure is then suddenly released to disintegrate the brash, amorphonsnoncork particles of the bark by reason of the explosive force of the expanding steam.

3 On the other hand, the softer cork layers in the bark are only softened further as a result of the steaming treatment and are only moderately reduced in size. Furthermore resiliency of the cork particles to some extent of heating moist woody material by any suitable means, for example, hot air, or by means of efiicient heat transfer from heated elements, such as fins. Steam pressures of about 200 to 600 psi. and cooking periods of about is actually improved as a result of the pufiing action of 5 30 to 90 seconds may be employed, although greater and the steam treatment. lesser pressures and cooking periods may be employed This operation may be carried out in any suitable depending upon the bark, its moisture content and other apparatus, for example, in a so-called Masonite gun, factors. Also, hot combustion gases may be employed such as used to fiberize wood chips for production of instead of steam as a source of heat, relying upon the hard board. Such apparatus is well known in the lumber moisture in the woody material to produce steam, which and wood products industries, and it requires no deappears to be essential for the selective disintegration tailed description herein. It consists essentially of a of the fibrous material. chamber with inlet means to introduce steam under pres- The procedure of the invention may be applied generalsure and an outlet which can be opened to blow out the ly to natural mixtures or agglomerates of cellular cork chips after they have been processed sufficiently within material and noncork material. Douglas fir bark, espethe chamber by means of high pressure steam. cially the thick bark from mature trees, is the preferred The steam pressure and temperature, and the duration starting material, but other barks which contain subof the processing or cooking operation may vary constantial amounts of cork may be employed, e.g., suitsiderably, as will be apparent from the examples below. ably selected bark from other firs, pines, spruce, hem- If conditions are not adequately severe, that is, if too low 106k, beech, maple and various species of oak. a pressure and temperature and/ or too short a cooking The practice and advantages of the present invention period is employed, the essential disintegrating effect of will be further illustrated by the following examples: the steam is not obtained. On the other hand, if conditions are too severe, that is, if too high a pressure and :EXAMPLE 1 temperature and/or too long a cooking period are employed, then it will be found that the steam disintegrates Douglas hark Containing large, Prominent Veins and causes excessive deterioration of the cork material, as layers of cork interspersed with y 0t rlolleerk well as the noncork material. From the description and tefial was p y as the starting materiai- This bark teachings contained herein, and with a modicum of trial was representative of thick Douglas fir hark from large, and error, conditions of pressure, temperature, and time tur tr s and was a commercial grade of bark which can be readily found to obtain optimum or approxiis in Pierltiful pp y at saw mills in the Douglas fir mately ptimum ult ber areas along the Pacific Coast, although the cork Aft r th ki step h b completed d h content was rather lower than average for Douglas fir mass of cooked product has been expelled or blown from bark available at the Particular mille fib o s m the cooking chamber, the cooked product can be dried erial predomin n amount, as is usuals bark by any suitable means, preferably by countercurrent conwas reduced in size y a PP t0 fragments averaging tact with a current of hot air. The dried, cooked prodabout X X 1%"- uct consists of a mass of disintegrated fibrous and amor- Approximately 130 Pounds of the bark were charged phous material which is predominantly small in particle to a gull 0f the yP described ab0Ve- Steam size, together with corky material which will also have was introduced until the pressure within the gun rose to been disintegrated or reduced in size but not nearly to 220 P- and was held at that Pressure or 3 S n sthe same degree as the noncork material. Moreover, this Then more steam was admitted until the Pressure corky material preserves substantially intact its original creased to 600 P' '2 such p requiring an additional porous cellular character and it constitutes an excellent 30 seeellds- The Outlet P which in this instance was material for insulation. The corky material is readily an Opening ah0i1t4 inches in diameter, was Opened wideseparated from the fibrous and amorphous, noncork ma- The steam Pressure within the gun blew the ts into ten'al by size classification, as by passing through a series a commercial drying system 110finally p y to y of screens of diminishing size. It will be found that the fiberized redwood for another P p e fl ent percentage of cork in the coarser fractions is much from the gun was a y moist, water-laden prediiet- It greater than in the original product, and that the perwas dried in the said commercial drying system y with centage of fibrous material is much greater in the finer tel'elll'rent Contact with hot air A Portion of the dried fractions. Such size classification or screening may be Product was separated into different size fractions, as carried out repeatedly, as by taking a given fraction and follows: subjecting it to a second screening. Also, the coarsest The y a was Passed through a Saree!!- fractions, e.g., material and if desired the -%"+8 Oversize material was rejected nd t mesh fraction may be recycled, i.e., given a second cookmaterial Was screened to yield +8, -8 +14, ing step, preferably under milder conditions. and fraetions- These frac- Steam is the preferred medium for cooking and selectiOIls w r s j t d to physical and Chemical tests with tively disintegrating woody material, and it is preferably results as given in Ta e I below. injected into the cooking chamber directly from a boiler. 0 However, steam y be generated in as y means A11 pressures herein are pounds per square inch gauge.

Table I Product of Example 1 Product of Example 2 Fraction +8 -8 +14 14+48 -18 +140 --140 +8 -8 +14 --14 +48 -48 -14!) wt 8.4 14.8 12.1 13.5 12.2 12.1 11.0 13.2 Bolub. in 1% NaOH, percent by wt 59.4 57.0 57.2 61.6 63.1 56.1 43.3 58,9 Solubllltyinethyl-alc.-. 21.9 24.5 22.2 31.9 23.8 24.4 21.3 31.3 Bulk density, #leu. 1t 18.1 17.0 18.1 25.0 29.7 18.1 17.0 18.1 25.0 29.1

EXAMPLE 2 An equal weight of chips taken from the same lot. as Example 1 was charged to the same Masonite gun and was treated in the same manner, except that after bringing the steam pressure in the gun to 600 p.s.i.g., it was held at that pressure for 60 seconds. The contents of the gun were then blown. A similar size classification was efiected and similar tests were applied, with results as given in Table I.

It will be apparent that the more severe conditions of Example 2 produced a higher proportion of finer material (l4 mesh) than the less severe conditions of Example 1. It will also be apparent that the finest fractions (l40) yielded the highest percentage of alcohol solubles. It was noted that all of the alcohol extracts precipitated a waxy, amorphous solid on cooling. It was further noted by visual inspection that the +8 mesh fraction contained particles of cork with fibrous material attached and that the +140 fraction was a black-brown, free-flowing powder.

A further sample of the product of Example 2 was screened to yield 4 +8, 8 +14, 14 +48, -48 +140 and 140 fractions. The coarest fraction was discarded. A visual inspection was made of the remaining fractions, with the aid of a microscope in the case of the finer fractions. The percentage of cork in each of these fractions was determined with substantial accuracy by hand separation, with results as follows:

Table II.-Crk concentration in various fractions as determined by hand separation Table II requires some explanation. Inspection of the 48 fractions by microscope revealed the presence of cork but in very small quantities and of particle sizes so small that hand separation was not deemed practical. The percent of total bark in line (2) excludes the discarded bark. This is considered justified because particles may be considered unprocessed and would be recycled in a continuous commercial process. Also, to some extent, these oversize particles were nonbark contaminants. Line (2), therefore, gives the quantity of each of the size fractions +8, 8 +14, 14 +48, 48 +140 and 140 expressed as a percentage of the total bark treated after separating the oversize material.

Line (3) gives the quantity of cork in each of the first three fractions, expressed as a percentage of that fraction. The figures in line (4) are arrived at by multiplying each of the figures in line (2) by the corresponding figure in line (3) expressed as a decimal; i.e., 15.3 0.67=10.3%, etc. Therefore the figures in line (4) represent the quantity of cork in each of the respective fractions, expressed as a percentage of the total bark. Line gives the quantity of cork in each of the first three fractions expressed as a percentage of the total cork in the bark. The figures in line (5) reflect a minor inaccuracy arising from the assumption that no cork existed in the 48 fractions. This inaccuracy was not of great magnitude. Microscopic inspection revealed very little cork in these fractions, and to a considerable extent the cork in these fractions existed as very small particles in the bark of so small a size as to have very limited commercial utility.

It will be seen from Table II that the first two frac- 6 tions, i.e., +8 and 8. +14, accounted for. 15 .3+7.8=23.l% of the total bark; that these two fractiOns contained cork in a concentration of and that these two fractions contained of the total cork in the bark, assuming a negligible quantity of cork in the 48 fractions.

It follows, therefore, that approximately one-half (53%) of the cork in the bark Was concentrated in approximately one-quaratcr (23.1%.) of the product consisting of the +8 and 8 +14 fractions.

The coarser fractions, particularly the +8 and -8 +14 fractions, are commercially useful without further processing. Thus these fractions, although they are not pure cork, are so enriched in cork that they can be used as insulation material in applications which donot require the highestquality of cork. Thus these fractions may be poured loose intoan insulating space heneath a floor, above a ceiling or in a wall space; A bindersuch as resin or asphalt may be employed to bind the particles together. The same fractions may also be used as fillers or extenders for other, more expensive insulating materials such as pure cork from the cork oak.

The finer fractions, such as the -48 +140 and l40 fractions also have utility, but of a somewhat different type. As mentioned above, by extracting these finer fractions with hot alcohol and cooling the extract, an amorphous waxy solid is produced which is similar to carnauba wax and other waxes of commerce; Also, surface active and dispersing agents can be prepared by extraction with caustic soda or other pulping agents.

It will, therefore, be apparent that the process of the present invention has utility generally as a means of separating cellular, corky material from fibrous and amorphous noncorky material contained in natural mixtures of the two such as Douglas fir bark.

As noted, the coarser fractions are enriched in cork but still contain a considerable proportion of noncork material. Most of the latter in the coarsest fractions +8) and (+8 +14) is present in the form of fibers and bundles or masses of fibers attached to the cork particles. Some, however, is present as separate fibers and bundles or masses of fibers. I have found that the attached fibers and fiber bundles and masses can be detached and ground, and that the already separated fibers and fiber bundles and masses can be ground by a relatively light milling operation, as by means of ball'or hammer milling or merely tumbling the particles and abrading them against one another. By such means, repeated several times if necessary, followed in each instance by size classification, it is possible to produce relatively coarse (+14) and pure (90-95%) cork.

Some further refinement, if carried out by gentle abrasion methods, yields a pure cork of high quality. The yield, of course, may be reduced. In commercial practice one will determine the optimum degree of refinement, suitably balancing the factors of economy and quality. The following example will illustrate the results obtainable by further refinement.

Table III Material Yield, Purity, percent percent Material (1) was the combined +8 and --8 +14 material originally produced as described in Example 2.

. 7 by steaming and blowing bark, drying, separating and rejecting +i material and screening the remainder without grinding. Material (2) was prepared by grinding material (1), then screening. The yield figure 23.1% for material (1) is explained above, and is based on the total bark after separating material. The yield figure 6.3% for material (2) was obtained by multiplying 23.1% by 27.1%, the latter being the percentage of ground material recovered as +14. The purity figures give the percentage of cork in each material.

It will be apparent from an inspection of Table III that an operator has the option of higher yields and less purity (e.g., a 23.1% yield and 66% purity) or lower yieldsand greater purity (e.g., a 6.3% yield and 80-85% purity).

The cork products of the invention may be put to many of the uses of cork from the cork oak; e.g., for thermal insulation, sound absorption, vibration damping, etc. The coarser grades of product may be ground to finer grades to produce insulation cork, composition cork, cork flour for linoleums, etc. And, of course, it may be used as a filler and extender material.

It will, therefore, be apparent that a method has been provided of treating natural cork-noncork mixtures such as Douglas fir bark to separate the cork from the noncork material, without serious damage to the cellular character of the cork. Such method is economical and can be carried out with existing commercial equipment presently in use in the lumber and wood products industries. It is versatile in that higher yields with'concomitant reduced quality, or better quality with reduced yields can be selected. The recovered cork is purer in quality than the corresponding material from other known processes of cork separation. Also the separated noncork material has commercial value.

We claim:

1. A method of cork recovery from bark containing a substantial proportion of cork which comprises providing the bark in the form of particles, subjecting said particles to the action of steam at an elevated pressure and for a short period of time, then releasing the pressure suddenly, thereby exploding a large proportion of the fiber masses into smaller fiber bundles and individual fibers, drying the exploded mass of fibers and cork and eifecting a size classification of the dried mass to produce coarser fractions enriched in cork and finer fractions poor in cork.

2. The method of claim 1 wherein said bark is Douglas fir bark.

3. A method as set forth in claim 1, wherein at least one of the coarser fractions is subjected to a gentle abrading action to further and selectively reduce the particle size of fibrous noncork material in such fraction, and wherein the abraded fraction is then subjected to a further size classification to yield a coarse fraction of higher cork content.

4. A method of treating bark containing a substantial quantity of cork in admixture with fibrous and amorphous noncork material, said method comprising providing the bark in the form of chips, subjecting the chips to the action of steam at a sufiiciently high pressure and for a sulficient period of time to soften the chips and loosen the bond between the cork and noncork material and thereby produce a loose mass interspersed with particles of cork when the steam pressure is suddenly released,- then releasing the steam pressure suddenly to explode the steam treated chips into a loose, moist mass of cork and noncork material, then drying the loose mass and subjecting it to size separation and recovering at least the +14 mesh fractions.

5. The method of claim 4 wherein said bark is Douglas fir bark.

6. The method of claim 4 wherein the chips are subjected to steam at about 600 p.s.i.g. for about 2 minutes.

References Cited in the file of this patent UNITED STATES PATENTS 2,446,551 Pauley Aug. 10, 1948 2,711,369 Birdseye June 21, 1955 2,736,063 Heritage Feb. 28, 1956 OTHER REFERENCES Marple: Douglas Fir Bark Utilized as a Filler, from Plastics, August 1947 (PP- 44, 65, 67). 

1. A METHOD OF CORK RECOVERY FROM BARK CONTAINING A SUBSTANTIAL PROPORTION OF CORK WHICH COMPRISES PROVIDING THE BARK IN THE FORM OF PARTICLES, SUBJECTING SAID PARTICLES TO THE ACTION OF STEAM AT AN ELEVATED PRESSURE AND FOR A SHORT PERIOD OF TIME, THEN RELEASING THE PRESSURE SUDDENLY, THEREBY EXPLODED A LARGE PROPORTION OF THE FIBER MASSES INTO SMALLER FIBER BUNDLES AND INDIVIDUAL FIBERS, DRYING THE EXPLODED MASS OF FIBERS AND CORK AND EFFECTING A SIZE CLASSIFICATION OF THE DRIED MASS TO PRODUCE COARSER FRACTIONS ENRICHED IN CORK AND FINER FRACTIONS POOR IN CORK. 